In recent years, research is conducted extensively and intensively in communication fields such as mobile communications and deep space communications as well as broadcasting fields such as ground-wave broadcasting and satellite digital broadcasting. Along with such research, there is also performed other research in a coding theory for the purpose of increasing the efficiencies of error-correction encoding and decoding processes.
As a theoretical limit of a communication-line encoding performance, there is known C. E. Shannon's limit given by so-called Shannon's communication line coding theorem.
The research in the coding theory is carried out for the purpose of developing a code exhibiting performance close to Shannon's limit. In recent years, as codes produced by encoding methods to exhibit performance close to Shannon's limit, for example, there have been developed the so-called Parallel Concatenated Convolutional Codes and the so-called Serial Concatenated Convolutional Codes, which are referred to hereafter simply as the PCCC and the SCCC respectively.
In recent years, on the other hand, there is also conducted research in methods of decoding these codes. To put it concretely, there is conducted research to decrease a symbol error rate by carrying out a soft-output operation on a decoded output of an internal code in concatenated codes and an output of each repetitive decoding operation adopting a repetitive decoding method. In addition, there is also extensively conducted research on decoding methods suitable for such codes. As a method to minimize a symbol error rate in a process to decode a predetermined code such as convolutional codes, for example, there are known a technique based on a BCJR algorithm and a technique based on a max-log-MAP algorithm and a log-MAP algorithm, which are each an improved BCR algorithm. The BCR algorithm is described by Bahl, Cocke, Jelinek and Raviv in a reference with a title of “Optimal decoding of Linear Codes for Minimizing Symbol Error Rate,” IEEE Trans. Inf. Theory, vol. IT-20, pp. 284–287, March 1974. On the other hand, the max-log-MAP algorithm and the log-MAP algorithm are described by Robertson, Villebrun and Hoeher in a reference with a title of “A Comparison of Optimal and Sub-Optimal MAP Decoding Algorithms Operating in the Domain,” IEEE Int. Conf. on Communications, pp. 1009–1013, June 1995. The max-log-MAP algorithm and the log-MAP algorithm are referred to hereafter as a max-log-BCJR algorithm and a log-BCJR algorithm respectively. The PCCC and the SCCC described above are decoded by carrying out the so-called repetitive decoding operation among a plurality of decoders, which carry out a MAP (Maximum A Posteriori) probability decoding process based on the BCR algorithm, the max-log-BCJR algorithm and the log-BCJR algorithm.
By the way, an encoding process is followed by signal-point mapping for bit data obtained as a result of the encoding process. The signal-point mapping is based on a multi-value modulation technique determined in advance. Examples of the multi-value modulation technique are an 8-PSK (Phase Shift Keying) modulation technique, a 16-QAM (Quadrature Amplitude Modulation) technique and a 64-QAM (Quadrature Amplitude Modulation) technique.
If an encoding process is followed by signal-point mapping based on the multi-value modulation technique determined in advance, however, it is impossible to make a margin for a noise of the encoded data completely match a margin for a noise found by the mapping. As a result, the transmission characteristics including a bit error rate deteriorate.
It is thus an object of the present invention addressing the problem described above to provide an information transmission apparatus and an information transmission method that are capable of implementing a high-performance encoding process with ease as a result of newly developing an encoding technique considered to be theoretically optimum for an encoding process adopting typically the multi-value modulation technique.
In addition, it is another object of the present invention to provide an information reception apparatus and an information reception method that are capable of easily decoding data obtained as a result produced by the information transmission apparatus and the information transmission method with a high degree of precision.